The present invention relates broadly to an analog to digital converter apparatus, and in particular to a two-bit analog to digital conversion apparatus without AGC.
An analog to digital converter apparatus is a device for converting information in the form of continuously varying signals into digital numbers which represent the magnitude of the signal at the time the conversion is made. In the most common applications, the converter is used to transform information into a form suitable for processing on a digital computer. This implies that analog information must be quantized into discrete voltage signals having an assigned logical 0 or 1 level (for example, ground, or +5 volts). The raw information frequently is taken from measurements of temperatures, forces, shaft rotation, or other continuous quantities and is first represented by an analog electrical signal, which is then converted to digital.
In the prior art, there are many techniques which can be used for analog-to-digital conversion. They range from simple-voltage-level comparators to complete close-loop conversion for high accuracy. The two techniques most commonly used are ramp counting and successive approximation. The counting method is a simple method but relatively slow for high-speed conversion systems. The analog signal to be converted is applied to one input terminal of a high-resolution comparator. The other input terminal to the comparator is connected to the output of a ramp generator. At the start of the ramp a binary counter is enabled and thereupon begins counting the master-clock pulses. When the ramp reaches the same level as the analog input signal, the counter is instructed to stop counting by the output of the comparator. The binary value in the counter is equivalent to the analog value. The total number of counts in one complete period of the ramp is equal to the number of quantization levels. The successive approximation has inherent in its principle of operation, a minimum number of switching networks to determine the analog value.